Analyses of the Effects of an Exotic Lizard (Anolis sagrei) on a Native Lizard (Anolis carolinensis) in Florida, Using Islands as Experimental Units

The green anole, Anolis carolinensis (Sauria: Polychrotidae), North America's only native anole, was abundant in even the most disturbed urban environs of Florida until recently. The Cuban brown anole, A. sagrei, was introduced to six Florida ports in the 1940s. Since then, it has become the most abundant lizard in peninsular Florida, has spread into Georgia and two other southeastern states, and has been blamed for the decline of A. carolinensis. Because A. carolinensis declines soon after the arrival of A. sagrei, it has been difficult to identify the mechanisms involved. I studied the effect of A. sagrei on A. carolinensis on dredge-spoil islands along the east coast of Florida. By introducing small numbers of A. sagrei to two very different islands, I contrasted their colonizing abilities, densities, and body conditions in two different habitat types. Stomach content analyses of the two species in sympatry indicated that they consume very similar proportions and taxa of arthropods, and that they consume each other's hatchlings in natural situations. In 1995, I introduced A. sagrei onto three islands occupied by A. carolinensis, and used three islands containing native A. carolinensis as controls. Over four summers, I monitored populations using capture-mark-recapture techniques, and collected body, microhabitat, and spatial data. Green anole densities and habitat parameters were similar over time on the controls. On the treatment islands, A. sagrei became dense in all habitat types, A. carolinensis declined as A. sagrei expanded, and survivors shifted their perch heights and utilized different habitats than they did prior to the introductions of A. sagrei. The decline was due to a lack of recruitment in subsequent years, suggesting that asymmetric intra-guild predation was involved in the rapid decline of green anoles. Sympatric green anole populations remained viable only in habitat patches containing dense understory vegetation, which may have provided more food and ameliorated the effects of hatchling predation Green anoles might remain viable in urban or disturbed environs where A. sagrei attains very high densities, as long as sufficient understory vegetation is present to ensure successful recruitment of hatchling green anoles to adulthood.